Great whites (Carcharodon carcharias) may live far longer than previously thought, according to a new study that used bomb radiocarbon dating to determine age.
Sharks are typically aged rather like counting tree rings, by counting growth band pairs deposited in their vertebrae. However, sharks grow more slowly as they get older and the band pairs become too thin to read. Age is then underestimated.
A new study by researchers at NOAA’s Northeast Fisheries Science Center (NEFSC) and the Woods Hole Oceanographic Institution used bomb radiocarbon dating on eight sharks caught between 1967 and 2010 in the Northwest Atlantic Ocean. This technique uses the discrete radiocarbon pulse in the environment caused by the detonation of nuclear bombs in the 1950s and 1960s as a “time stamp”. Radiocarbon levels incorporated into the band pairs are measured and related to a reference chronology to determine the absolute age of a fish.
Of the eight sharks studied, the oldest was found to be 73 when it died. In all previous studies of shark lifespan, no shark was estimated to be over 23 years old.
White sharks are considered vulnerable under the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Although the Great White Shark is such a famous species of fish, very little is known about its biology. Its maximum size remains a matter of debate. Some estimate around 6 m and others 6.4 m or more. Lengths and ages at maturity for both sexes remain undetermined. A mature female of 500 cm was estimated to have reached around 14 to 16 years, but that was when the oldest individual reported was a female assumed to be not much more than 23. The real age at maturity may be much older.
The study hints at possible sexual dimorphism in growth rates, and raises concerns that white shark populations are considerably more sensitive to human-induced mortality than previously thought.
With lifespan estimates of 70 years and more, white sharks may be among the longest-lived fishes. Sharks that mature late, have long life spans and produce small litters have the lowest population growth rates and the longest generation times. Increased age at maturity would make white sharks more sensitive to fishing pressure than previously thought, given the longer time needed to rebuild white shark populations.
Hamady LL, Natanson LJ, Skomal GB, Thorrold SR (2014) Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks. PLoS ONE 9(1): e84006. doi:10.1371/journal.pone.0084006
Fergusson, I., Compagno, L.J.V. & Marks, M. 2009. Carcharodon carcharias. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. . Downloaded on 10 January 2014.
Radiocarbon Dating Suggests White Sharks Can Live 70 Years and Longer, NOAA
Photo credit: Terry Goss, CC BY-SA 3.0